1. Technical Field
The present disclosure relates to a vehicle lamp lighting control device and particularly to a vehicle lamp lighting control device that controls a lighting operation of a semiconductor light source including a semiconductor light emitting element.
2. Related Art
A known vehicle lamp incorporates a semiconductor light emitting element such as an LED (Light Emitting Diode) as a semiconductor light source. This kind of vehicle lamp is equipped with a lighting control device that controls a lighting operation of the LED.
This kind of lighting control device has a current limiting circuit to protect the semiconductor light source when a large current pulse (load dump) flows from an in-vehicle battery to the semiconductor light source upon starting the vehicle (see, e.g., JP-A-2004-122912).
For implementations in which a power supply voltage supplied to a resistor connected in series to the semiconductor light source is equal to or more than a predetermined voltage, the current limiting circuit decreases a current flowing to the resistor. Accordingly, when an overvoltage caused by a dump surge or the like is applied to the lighting control device, the current flowing from the positive electrode of the power supply to the resistor decreases, to prevent damage to the semiconductor light source.
As described above, in the known vehicle lamp, it is possible to prevent damage to the semiconductor light source as a result of an overvoltage by using the current limiting circuit.
However, if the positive electrode of the power supply is in a ground fault condition, a battery voltage is short-circuited to GND (ground), so that a large ground fault current flows from the positive electrode to ground. As a result, the lighting control device may be damaged.